Most interactive projectors, such as Epson BrightLink 595Wi and its similar products, have to project images onto a flat surface during calibration. The calibration might fail if the projection surface is not flat enough or is partially covered by some objects. Those projectors could not automatically sense the projection area during calibration, the projection area is manually marked by users instead. Even the professionals need to spend a lot of time in adjusting the projector's position and repeating the calibration steps several times to complete the calibration. Because the calibration is pretty time-consuming, those projectors are usually installed in a fixed position to avoid re-calibration. Such kind of calibration method is not suitable for a portable interactive projection device that moves often.